Background The aim of this study was to investigate suicidal ideations and associated psychopathology in two groups of adolescents, a sample of detained youth and a general population sample. In both groups the comparisons of mental health characteristics between suicidal ideators and non-suicidal youth were conducted separately for girls and boys. Methods The study sample consisted of 290 delinquent adolescents [228 boys and 62 girls] from three Flemish juvenile detention centers and 1,548 adolescents [811 boys and 737 girls] from an age-matched school-based sample. Both groups were administered the Social and Health Assessment [SAHA], a self-report survey investigating levels of psychopathology [internalizing and externalizing] and risk-taking behavior. Results Suicidal ideations during the past year were reported by 21.5% of detained males, compared to 6.7% in the general population. In females, 58.1% of detained individuals reported suicidal thoughts during the past year, compared to 14.4% of the general population. In girls and boys from the general population, both internalizing and externalizing problems were higher in suicidal ideators than in non-suicidal youth, while in the detention group mainly internalizing problems were higher in suicidal ideators. When comparing detention suicidal ideators with those from the general population, male suicidal ideators scored higher on delinquency, while detained female suicidal ideators also scored higher on posttraumatic stress, but lower on prosocial beliefs. Limitations Information used in this study was solely based on self-report measures only and limited to Flemish adolescents. Conclusion Since suicidal ideation is a frequent problem in detained youth, adequate recognition and treatment seems clinically relevant. While both internalizing and externalizing psychopathology may be an indicator of suicidal ideation in the general population, internalizing problems may be the main clinical predictor in detained youth.